1. Field of the Invention
The present invention relates to a semiconductor device having a memory device that has a pair of electrodes and memory material layers stacked therebetween, and an operating method thereof.
2. Description of the Related Art
Conventionally, a memory device with a multilayer structure has been proposed in order to increase a memory capacity (see Patent Document 1). Patent document 1 discloses a memory device having a memory portion composed of multiple memory cells that are arranged in a two-dimensional matrix, which is formed by staking memory layers.
In addition, such a multilayered memory device that has a stable organic-layered element with a multilayer structure has been proposed, which has a pair of electrodes and layers stacked therebetween, where the stacked layers include two or more organic thin films each having a different dielectric constant (see Patent Document 2).
However, as disclosed in Japanese Patent Laid-Open No. 2001-345431 (Patent Document 3) that is disclosed in Patent Document 2, a memory element utilizing such organic ferroelectric thin films has a problem in that a dielectric breakdown occurs when an opposite electric field is applied thereto.    [Patent Document 1] Japanese Patent Laid-Open No. 2002-26283    [Patent Document 2] Japanese Patent Laid-Open No. 2004-304180    [Patent Document 3] Japanese Patent Laid-Open No. 2001-345431
In the case of a memory device having a multilayer structure as shown in Patent Document 1, the thickness of the device itself is increased. Since a memory device is often mounted as a component of an electronic appliance, the increased thickness of the device will restrict the layout of the device. Further, since each layer of a memory element in the memory device is required to be connected to a driver circuit, the circuit configuration becomes complex.
Patent Document 2discloses a stable organic-layered memory element and a memory device and a driving method of these, where a difference between the threshold voltage for writing data and the threshold voltage for erasing data can be varied. Patent document 3 poses a problem in that a dielectric breakdown might occur when an opposite electric field is applied.